Commercial aircraft generally include an upper lobe, e.g. passenger cabin, and lower lobe, e.g. cargo bay. In order to maintain a desired pressure differential between the upper and lower lobes, air pathways are often provided around the perimeter of a passenger cabin floor structure. Typically, a positive air pressure differential is maintained between the upper and lower lobes. That is, the air pressure in the upper lobe is generally higher than the air pressure in the lower lobe. More specifically, air is forced from the lower lobe to the upper lobe though a suitable duct system. Then, because the air pressure in the upper lobe is higher than the air pressure in the lower lobe, the air from the upper lobe is forced through the air pathways to the lower lobe.
In at least one known aircraft architecture, the air pathways are provided by openings between cross members of shear trusses that connect the aircraft fuselage structure to the passenger cabin floor structure. The air pathways are sized so that they will allow a sufficient flow of air from the upper lobe to the lower lobe to maintain the desired air pressure differential during normal operation of the aircraft. The air pathways are further sized such that during the occurrence of rapid decompression of the aircraft extremely large amounts of air will be allowed pass between the upper and lower lobes very quickly. Occurrences of rapid decompression are generally caused by a breach of the integrity of the outer skin of the air craft, e.g. a cargo bay door being dislodged. The rapid passage of large amounts of air allows the pressure differential between the upper and lower lobes to be rapidly reduced to approximately zero. This prevents the floor structure from buckling and causing damage to the fuselage structure during an occurrence of rapid decompression. However, noise from the lower lobe easily passes through these air pathways and can be bothersome to passengers in the upper lobe.
Therefore, it is extremely desirable to provide a noise barrier to minimize the transmission of noise from the lower lobe to the upper lobe through the air pathways. It is further extremely desirable to provide such a barrier that will not only allow sufficient air to flow from the upper lobe during normal operation but will also allow extremely large amounts of air to rapidly pass between the upper and lower lobes during rapid decompression of the aircraft.